1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a semiconductor device and method of fabricating the same, capable of preventing generation of a moat at the top corners of the device isolation film.
2. Background of the Related Art
In all the semiconductor devices, a device isolation film is formed in order to electrically isolate various elements. Conventionally, the device isolation film is formed by means of a LOCOS (local oxidation) process. In this case, however, there are problems that electrical characteristics of the device and the degree of integration are degraded due to a bird's beak occurred at the corner of the device isolation film.
As the degree of integration in the semiconductor devices becomes higher, the device isolation film is formed to have a STI (shallow trench isolation) structure in order to prevent generation of the bird's beak in the device isolation film and also minimize the area occupied by the device isolation film.
In case where the device isolation film is formed to have the STI structure, there is a problem that a moat occurs at the top corners of the device isolation film in the etch process for removing the pad nitride film being the hard mask and in a gate oxide pre-cleaning process.
FIG. 1 is a SEM (scanning electron microscope) photograph illustrating that a moat occurred at the top corners of the device isolation film.
From FIG. 1, it can be seen that the top corners of the device isolation film are etched and the moat is thus formed, in the etch process for removing the pad nitride film being the hard mask and in a gate oxide pre-cleaning process. If the moat is formed at the top corners of the device isolation film as such, etched materials remain at the moat in the process of patterning a conductive material layer in order to form a gate, which causes defects and degrades the electrical characteristics and reliability of the device. Furthermore, as the corner of the active region in the semiconductor substrate in which the semiconductor device is formed is pointed, the gate oxide film is thinly formed at the pointed portion. For this reason, the leakage current is generated and the threshold voltage of the device is changed, at the portion where the gate oxide film is thinly formed, which results in degrading reliability and electrical characteristics of the device.
Furthermore, as the design rule becomes small and the width of the MOSFET device is narrowed, the ratio of the area that the gate oxide film is thinly formed compared to a total area of the active region is relatively increased. Due to this, an electric field is concentrated on the portion where the gate oxide film is thinly formed and a fatal problem such as INWE (inverse-narrow width effect), etc. may thus occur.